In general, a three-dimensional image is formed on the basis of stereoscopy as perceived through the two eyes of a person. The most important factor of the three-dimensional effect is the binocular disparity caused by the distance of about 65 mm between the two eyes. That is, by allowing a left eye image to be recognized only via the left eye and a right eye image to be recognized only via the right eye, an observer may experience binocular disparity due to a difference between the left eye image and the right eye image, and thus recognize a three-dimensional image.